Methods, systems, and devices for intra-scan motion correction

ABSTRACT

Systems, methods, and devices for intra-scan motion correction to compensate not only from one line or acquisition step to the next, but also within each acquisition step or line in k-space. The systems, methods, and devices for intra-scan motion correction can comprise updating geometry parameters, phase, read, and/or other encoding gradients, applying a correction gradient block, and/or correcting residual errors in orientation, pose, and/or gradient/phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/527,972, filed Aug. 26, 2011, and titled DYNAMIC ADJUSTMENT OFMAGNETIC FIELD GRADIENTS AND RF PULSES WITHIN MR SEQUENCES, which ishereby incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

This invention was made with government support under Grant Number5R01DA021146 awarded by the National Institutes of Health. Thegovernment has certain rights to this invention.

BACKGROUND

Field

This invention relates generally to the field of biomedical imaging, andmore specifically to a system for correcting defects in medical imagesthat are caused by a subject's movement during an in vivo (in the livingbody) magnetic resonance scan.

Description

“Tomographic” imaging techniques generate images of multiple slices ofan object. Some commonly used tomographic imaging techniques includemagnetic resonance imaging (MRI) and magnetic resonance spectroscopy(MRS) techniques, which are ideal for assessing the structure,physiology, chemistry and function of the living brain and other organs,in vivo and non-invasively. Because the object of interest is oftenimaged in many scanning steps in order to build a complete two or threedimensional view, scans are of long duration, usually lasting severalminutes. To increase resolution (detail) of a tomographic scan, moreslices and more scanning steps must be used, which further increases theduration of a scan. Scans may also be of long duration in order toobtain sufficient signal-to-noise ratio. Magnetic resonance techniques(including tomographic techniques), that are currently known or to bedeveloped in the future (hereinafter collectively referred to as “MR” or“MRI”) can also afford relatively high spatial and temporal resolution,are non-invasive and repeatable, and may be performed in children andinfants. However, due to their duration, MR scans can be subject to theproblem of patient or object motion.

SUMMARY

Advancements in magnetic resonance technology make it possible tocorrect for artifacts in images obtained from magnetic resonance scanswhich are caused by motion of the subject during the magnetic resonancescan.

In some embodiments, a magnetic resonance system configured to correctintra-scan motion during a magnetic resonance scan comprises: a magneticresonance scanner configured to generate a magnetic field gradient and aradiofrequency signal for the magnetic resonance scan; a motion trackingsystem configured to track one or more pose parameters of a subject andtransmit pose data corresponding to the tracked one or more poseparameters at a given time to the magnetic resonance scanner, anelectronic memory storage configured to store modules; and a computerprocessor configured to execute the modules comprising at least: acorrection gradient calculation module configured to calculate a momentof a correction gradient to apply to the subject, wherein the moment ofthe correction gradient is calculated based on the transmitted pose dataand a gradient sequence used for the magnetic resonance scan; themagnetic resonance scanner further configured to apply the correctiongradient to the subject prior to detecting signals emitted from thesubject to correct one or more initial errors in magnetic gradientmoment due to movement of the subject during the magnetic resonancescan; and the magnetic resonance scanner further configured to detectthe signals emitted from the subject for data acquisition.

In certain embodiments, an intra-scan motion correction systemcomprises: an electronic memory storage configured to store modules; anda computer processor configured to execute the modules comprising atleast: a motion tracking module configured to receive pose data of asubject from one or more motion tracking systems during a magneticresonance scan of the subject; and a correction gradient calculationmodule configured to calculate a moment of a correction gradient toapply to the subject, wherein the moment of the correction gradient iscalculated based on the received pose data and a gradient sequence usedfor the magnetic resonance scan, and wherein the correction gradient isto be applied to the subject to correct one or more initial errors inmagnetic gradient moment due to movement of the subject during themagnetic resonance scan.

In some embodiments, an intra-scan motion correction system comprises:an electronic memory storage configured to store modules; and a computerprocessor configured to execute the modules comprising at least: amotion tracking module configured to receive pose data of a subject fromone or more motion tracking systems over a computer network during amagnetic resonance scan of the subject; and an error correction moduleconfigured to calculate a gradient moment based on the received posedata and a gradient sequence used for the magnetic resonance scan,wherein the error correction module is further configured to correct oneor more errors in the calculated gradient moment, and wherein the one ormore errors in the gradient moment are corrected during reconstruction.

In some embodiments, an intra-scan motion correction system comprises:an electronic memory storage configured to store modules; and a computerprocessor configured to execute the modules comprising at least: amotion tracking module configured to receive pose data of a subject fromone or more motion tracking systems over a computer network during amagnetic resonance scan of the subject; and an error correction moduleconfigured to calculate a phase based on the received pose data and agradient sequence used for the magnetic resonance scan, wherein theerror correction module is further configured to correct one or moreerrors in the phase, and wherein the one or more errors in the phase arecorrected during reconstruction.

In some embodiments, a computer-implemented method of correcting forintra-scan motion during a magnetic resonance scan comprises: generatingby a magnetic resonance scanner a magnetic field gradient and aradiofrequency signal for the magnetic resonance scan; tracking by amotion tracking system one or more pose parameters of a subject andtransmitting pose data corresponding to the tracked one or more poseparameters at a given time to the magnetic resonance scanner;calculating by a correction gradient calculation module a moment of acorrection gradient to apply to the subject, wherein the moment of thecorrection gradient is calculated based on the transmitted pose data anda gradient sequence used for the magnetic resonance scan; applying bythe magnetic resonance scanner the correction gradient to the subjectprior to detecting signals emitted from the subject to correct one ormore initial errors in magnetic gradient moment due to movement of thesubject during the magnetic resonance scan; and detecting by themagnetic resonance scanner the signals emitted from the subject for dataacquisition, wherein the computer comprises a computer processor and anelectronic storage medium.

In certain embodiments, a computer-implemented method of correcting forintra-scan motion during a magnetic resonance scan comprises: receivingby a motion tracking module pose data of a subject from one or moremotion tracking systems during the magnetic resonance scan of thesubject; and calculating by a correction gradient calculation module amoment of a correction gradient to apply to the subject, wherein themoment of the correction gradient is calculated based on the receivedpose data and a gradient sequence used for the magnetic resonance scan,and wherein the correction gradient is to be applied to the subject tocorrect one or more initial errors in magnetic gradient moment due tomovement of the subject during the magnetic resonance scan, wherein thecomputer comprises a computer processor and an electronic storagemedium.

In some embodiments, a computer-implemented method of correcting forintra-scan motion during a magnetic resonance scan comprises: receivingby a motion tracking module pose data of a subject from one or moremotion tracking systems over a computer network during a magneticresonance scan of the subject; and calculating by an error correctionmodule a gradient moment based on the received pose data and a gradientsequence used for the magnetic resonance scan, wherein the errorcorrection module is further configured to correct one or more errors inthe calculated gradient moment, and wherein the one or more errors inthe gradient moment are corrected during reconstruction, wherein thecomputer comprises a computer processor and an electronic storagemedium.

In some embodiments, a computer-implemented method of correcting forintra-scan motion during a magnetic resonance scan comprises: receivingby a motion tracking module pose data of a subject from one or moremotion tracking systems over a computer network during a magneticresonance scan of the subject; and calculating by an error correctionmodule a phase based on the received pose data and a gradient sequenceused for the magnetic resonance scan, wherein the error correctionmodule is further configured to correct one or more errors in the phase,and wherein the one or more errors in the phase are corrected duringreconstruction, wherein the computer comprises a computer processor andan electronic storage medium.

In some embodiments, a computer-readable, non-transitory storage mediumhas a computer program stored thereon for causing a suitably programmedcomputer system to process by one or more computer processorscomputer-program code by performing a method to correct for intra-scanmotion during a magnetic resonance scan when the computer program isexecuted on the suitably programmed computer system, wherein the methodcomprises: generating by a magnetic resonance scanner a magnetic fieldgradient and a radiofrequency signal for the magnetic resonance scan;tracking by a motion tracking system one or more pose parameters of asubject and transmitting pose data corresponding to the tracked one ormore pose parameters at a given time to the magnetic resonance scanner;calculating by a correction gradient calculation module a moment of acorrection gradient to apply to the subject, wherein the moment of thecorrection gradient is calculated based on the transmitted pose data anda gradient sequence used for the magnetic resonance scan; applying bythe magnetic resonance scanner the correction gradient to the subjectprior to detecting signals emitted from the subject to correct one ormore initial errors in magnetic gradient moment due to movement of thesubject during the magnetic resonance scan; and detecting by themagnetic resonance scanner the signals emitted from the subject for dataacquisition, wherein the computer comprises a computer processor and anelectronic storage medium.

In certain embodiments, a computer-readable, non-transitory storagemedium has a computer program stored thereon for causing a suitablyprogrammed computer system to process by one or more computer processorscomputer-program code by performing a method to correct for intra-scanmotion during a magnetic resonance scan when the computer program isexecuted on the suitably programmed computer system, wherein the methodcomprises: receiving by a motion tracking module pose data of a subjectfrom one or more motion tracking systems during the magnetic resonancescan of the subject; and calculating by a correction gradientcalculation module a moment of a correction gradient to apply to thesubject, wherein the moment of the correction gradient is calculatedbased on the received pose data and a gradient sequence used for themagnetic resonance scan, and wherein the correction gradient is to beapplied to the subject to correct one or more initial errors in magneticgradient moment due to movement of the subject during the magneticresonance scan, wherein the computer comprises a computer processor andan electronic storage medium.

In some embodiments, a computer-readable, non-transitory storage mediumhas a computer program stored thereon for causing a suitably programmedcomputer system to process by one or more computer processorscomputer-program code by performing a method to correct for intra-scanmotion during a magnetic resonance scan when the computer program isexecuted on the suitably programmed computer system, wherein the methodcomprises: receiving by a motion tracking module pose data of a subjectfrom one or more motion tracking systems over a computer network duringa magnetic resonance scan of the subject; and calculating by an errorcorrection module a gradient moment based on the received pose data anda gradient sequence used for the magnetic resonance scan, wherein theerror correction module is further configured to correct one or moreerrors in the calculated gradient moment, and wherein the one or moreerrors in the gradient moment are corrected during reconstruction,wherein the computer comprises a computer processor and an electronicstorage medium.

In some embodiments, a computer-readable, non-transitory storage mediumhas a computer program stored thereon for causing a suitably programmedcomputer system to process by one or more computer processorscomputer-program code by performing a method to correct for intra-scanmotion during a magnetic resonance scan when the computer program isexecuted on the suitably programmed computer system, wherein the methodcomprises: receiving by a motion tracking module pose data of a subjectfrom one or more motion tracking systems over a computer network duringa magnetic resonance scan of the subject; and calculating by an errorcorrection module a phase based on the received pose data and a gradientsequence used for the magnetic resonance scan, wherein the errorcorrection module is further configured to correct one or more errors inthe phase, and wherein the one or more errors in the phase are correctedduring reconstruction, wherein the computer comprises a computerprocessor and an electronic storage medium.

For purposes of this summary, certain aspects, advantages, and novelfeatures of the invention are described herein. It is to be understoodthat not necessarily all such advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves one advantage or groupof advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features, aspects and advantages of the presentinvention are described in detail below with reference to the drawingsof various embodiments, which are intended to illustrate and not tolimit the invention. The drawings comprise the following figures inwhich:

FIG. 1A depicts an example illustrating the effects of motion of asubject during a magnetic resonance scan by a conventional MRI system.

FIG. 1B depicts an example illustrating the effects of motion of asubject during a magnetic resonance scan by an adaptive MRI system.

FIG. 2 illustrates the effects of motion of a subject during a magneticresonance scan in k-space.

FIG. 3 depicts an example of one embodiment of an intra-scan motioncorrection system coupled with a magnetic resonance scanner.

FIG. 4 is a time frame diagram illustrating an example of embodiments ofone or more methods of intra-scan motion correction during a magneticresonance scan.

FIG. 5 is a process flow diagram illustrating an example of anembodiment of an update geometry parameters block of an embodiment of amethod of intra-scan motion correction during a magnetic resonance scan.

FIG. 6 is a process flow diagram illustrating an example of anembodiment of an update phase and/or read encoding gradient(s) block ofan embodiment of a method of intra-scan motion correction during amagnetic resonance scan.

FIG. 7 is a process flow diagram illustrating an example of anembodiment of an apply correction gradient block of an embodiment of amethod of intra-scan motion correction during a magnetic resonance scan.

FIG. 7A is a process flow diagram illustrating an example of anembodiment of an apply correction phase block of an embodiment of amethod of intra-scan motion correction during a magnetic resonance scan.

FIG. 8 is a process flow diagram illustrating an example of anembodiment of an error correction block of an embodiment of a method ofintra-scan motion correction during a magnetic resonance scan.

FIG. 9 is a schematic diagram illustrating the effects of an example ofan embodiment of a method of intra-scan motion correction during amagnetic resonance scan.

FIG. 10 is a schematic diagram illustrating the effects of an example ofan embodiment of a method of intra-scan motion correction during amagnetic resonance scan.

FIG. 11 is a block diagram depicting one embodiment of a computerhardware system configured to run software for implementing one or moreembodiments of the continuous intra-scan motion correction systemsdescribed herein.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with reference to theaccompanying figures. The terminology used in the description presentedherein is not intended to be interpreted in any limited or restrictivemanner, simply because it is being utilized in conjunction with adetailed description of certain specific embodiments of the invention.Furthermore, embodiments of the invention may comprise several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the inventions hereindescribed.

The disclosure herein provides methods, systems, and devices forintra-scan motion correction during a magnetic resonance (MR) scan.

As used herein, the terms “magnetic resonance techniques,” “magneticresonance imaging,” “magnetic resonance scan,” “MR techniques,” “MRimaging,” “MR scan” are broad interchangeable terms, and comprisewithout limitation magnetic resonance scan, magnetic resonance imaging,functional magnetic resonance imaging, diffusion magnetic resonanceimaging, magnetic resonance tomographic techniques, magnetic resonancespectroscopy, other magnetic resonance-based techniques currentlyexisting or to be developed in the future, and/or combinations thereof.

Further, as used herein, the terms “intra-scan motion correction,”“intra-sequence motion correction,” “continuous intra-scan motioncorrection,” “substantially continuous intra-scan motion correction,”“nearly continuous intra-scan motion correction,” “repeated intra-scanmotion correction,” “rapidly repeated intra-scan motion correction,” and“quasi-continuous intra-scan motion correction” are broadinterchangeable terms, and comprise without limitation single, one ormore, continuous, quasi-continuous, substantially continuous, nearlycontinuous, repeated corrections or the like for one or more errors dueto motion of a subject during a magnetic resonance scan, wherein thecorrections are applied during the magnetic resonance scan for anymagnetic resonance techniques. In addition, as used herein, the terms“real time,” “near real time,” and “substantially real time” are broadinterchangeable terms, and comprise without limitation real time, nearreal time, or substantially real time periods with minimal delay or lag,for example instantaneously, within 20-30 milliseconds, and/or within2-3 seconds or longer.

Because certain magnetic resonance techniques require that so manymeasurements be taken (because so many slices and/or scanning steps arenecessary), MR scans typically have a long duration, so that motion ofthe subject is a substantial problem for acquiring accurate data.Consequently, subjects commonly are required to lie still to within onemillimeter and one degree (better than the image resolution) overextended time periods. These strict requirements cannot be met by manysubjects in special populations, such as children and infants, patientswith stroke, head trauma, dementia, very sick patients, subjects who areagitated or delirious perhaps due to anxiety or drug use, animals, orpatients with movement disorders, resulting in data with motionartifacts. As a result, in order to perform an MR scan in such subjects,anesthesia can be required. However, anesthesia can cost about $900 andalso has roughly 1/250,000 risk of death.

Further, many tomographic imaging techniques rely on detecting verysmall percentage changes in a particular type of signal, which makesthese techniques even more susceptible to movement. In functionalmagnetic resonance imaging, for example, changes in the properties ofblood in brain areas activated while subjects are performing taskscauses small signal changes (on the order of a few percent) that can bedetected with MR. However, these small signal changes may easily beobscured by signal changes of similar or even greater size that occurduring unintentional subject movements.

The basic problem is that it may take several minutes for a scan to becompleted, but the patient or other object being scanned cannot remainsufficiently still for several minutes. Further, the space for a patientor other object being scanned (the “scanning volume”) in an MR machineis very limited—there is very little space in an MR machine once apatient has been positioned inside for a scan. The motion during thescan of a single dataset (e.g. spectrum, 2D-slice, multiple slices or3D-volume) causes the single acquisition steps to become inconsistent.Since the resulting data are reconstructed from many acquisition steps,this inconsistency can lead to significant data errors, called motionartifacts.

For example, at any given hospital or medical facility, 1 out of every25 brain examinations can be lost entirely and 1 out of 2 examinationscan require at least one repeat scan. The total economic loss tohospital in the U.S. due to such motion artifacts is estimated to beroughly 1.5 million hours per year or $1 billion annually at $750 perhour.

However, by implementing one or more methods, systems, and devices forintra-scan motion correction as described herein, subjects of a magneticresonance scan are not required to lie still. Rather, because themethods, systems, and devices for intra-scan motion correction asdescribed herein are able to account for movements in subjects ofvarying degrees and speed, substantially any movement by a subjectduring a magnetic resonance scan. In some embodiments, substantially anymovement by a subject that can be approximated by a local rigid bodymotion and/or nearly rigid body motion in the area or object of interestcan be accounted for. In certain embodiments, any motion of a subject orwithin a subject that can be described by a motion path that can beapproximated by a rigid body can be take into account.

In some embodiments, the methods, systems, and devices for intra-scanmotion correction can allow for magnetic resonance scan techniques,whether existing now or to be developed in the future, to be applied tomany subjects, including those in special populations, such as children,infants, very sick patients, subjects who are agitated perhaps due toanxiety or drug use, or patients with movement disorders. In addition,effects of movements of certain objects located within a subject, suchas internal organs of a subject, fetus, or the like, can also becorrected for in certain embodiments. Further animals may also besubjected to a magnetic resonance scan by implementing one or moremethods, systems, and devices for intra-scan motion correction asdescribed herein. Additionally, inanimate objects that move, includingflowing liquids or gases, may also be subjected to a magnetic resonancescan by implementing one or more methods, systems, and devices forintra-scan motion correction as described herein. In addition, themethods, systems, and devices for intra-scan motion correction cansubstantially reduce the economic loss described above due to motionartifacts.

In addition, in some embodiments, the methods, systems, and devices forintra-scan motion correction as described herein do not require thatgradients track the rotation of the object of interest as other certainembodiments do or attempt to do. Rather, in some embodiments of themethods, systems, and devices for intra-scan motion correction asdescribed herein, gradient rotations are specifically not updated withina single scan (between excitation and data acquisition). In other words,gradients remain stationary and do not track the motion of the subjectto be scanned in some embodiments. The result is that at the end of thesequence, the Bloch equations governing magnetic resonance are notsatisfied in some situations, which can introduce an error in thegradient moment. Some embodiments of the methods, systems, and devicesfor intra-scan motion correction as described herein can unexpectedlyeliminate such error in the gradient moment by applying a single, brief,correction gradient of proper gradient moment prior to data acquisition.

Further, in general, subject movement can comprise rotations and/ortranslations. Rotation matrices can be non-linear, due to the presenceof sine and cosine terms. Therefore, if the Bloch equations are violatedin some embodiments by not having gradients track subject movement, onemight expect that the resulting phase errors become “non-linear” inspace, and consequently cannot be corrected using linearly varyinggradients. However, theoretical analysis demonstrates that one can uselinear gradients to correct the resulting. Accordingly, in someembodiments, the methods, systems, and devices for intra-scan motioncorrection as described herein can correct for motion artifacts not onlydue to translations, but also due to small and/or large rotationswithout having gradients track subject movement.

Moreover, some embodiments of the methods, systems, and devices forintra-scan motion correction as described herein can be simple and notrequire a substantial amount of data processing. For example, in someembodiments, only one or more additional processes are required inaddition to a general magnetic resonance scan process in order tocorrect for subject motion during the magnetic resonance scan.Accordingly, implementation of some embodiments of the methods, systems,and devices for intra-scan motion correction as described herein can berelatively easy and can be implemented in conjunction any and/or allexisting magnetic resonance scan equipment and/or those to be developedin the future. Accordingly, the methods, systems, and devices forintra-scan motion correction as described herein can provide anunexpectedly simple yet accurate correction for any and/or all types ofsubject motion during a magnetic resonance scan.

Reducing Sensitivity of Scans to Motions of Subject

In some embodiments, specially designed scan sequences can be utilizedto minimize the effects of constant motion during a single acquisitionstep without relevant organ shift during the entire acquisition. Forexample, a first order flow compensation can be utilized. While suchembodiments are particularly useful for reducing artifacts or imagingerrors due to flowing blood they are not particularly useful incorrecting movements of entire organs, such as head movements.

In other embodiments, improved sampling schemes for the magneticresonance data can be used to reduce sensitivity to motion. Suchembodiments can reduce motion sensitivity of magnetic resonance scansunder certain conditions. However, they are not particularly useful incorrecting motions under other conditions or for very quick movements.Further such embodiments can require redundant measurements to encodeadditional information required for correction and thus reduce samplingefficiency. Such embodiments are also not generally applicable to allmeasurement techniques.

In certain embodiments, certain ultra-fast single shot imagingtechniques can be utilized to account for movement by a subject during amagnetic resonance scan. For example, echo planar imaging, spiralimaging, or imaging using other fast trajectories can be utilized. Insuch embodiments the entire organ of interest, such as a brain, isscanned continuously every few seconds over the course of minutes, forinstance, for functional magnetic resonance imaging, diffusion imaging,perfusion imaging, or other modalities. By doing so, such embodimentsmake it possible to determine the pose defined as a position androtation, for example of the head or other subject at each instantrelative to the initial pose, using image-based registration and/oralignment of images. More specifically, once the pose for a giveninstant is known relative to the initial image, the magnetic resonancescanner's image for that instant can be realigned to the initial image.Further, realignment of magnetic resonance imaging volumes comprisingmultiple slices can be used to correct for head motion and functionalmagnetic resonance imaging time series. However, such embodiments areinherently slow because they use magnetic resonance imaging and may beunable to correct for motion in certain directions, such as orthogonalto the scan planes or towards or away from the planes in which the scansare being taken. Also, such embodiments correct movements only every fewseconds (for each volume).

Motion Correction Methods

The embodiments for reducing sensitivity of scans to motions of asubject described above, however, are rather limited. One major problemis related to the manner in which typical tomographic imaging methodsacquire data. Specifically the data for each cross section or slice isacquired by moving step by step along lines in a mathematical space,also known as k-space. This data acquisition step is typically repeatedhundreds of times in a magnetic resonance imaging scan, until all linesin the k-space have been filled. For three dimensional imaging,thousands of such steps are required to acquire an entire volume. Thevarious embodiments of reducing sensitivity of scans to subject motion,however, typically do not account for variations in the subject's poseamongst the different k-space lines, even though motion sensitivity foreach individual acquisition or a line in k-space is reduced. Further,the various embodiments of reducing sensitivity of scans to motions of asubject rather poorly tolerate fast or irregular movements withinindividual acquisition steps.

Accordingly, in some embodiments, the pose of the subject of the scanand motion is tracked near-real time, during a scan. For example, thesubject can be a head, brain, or other organ of interest or otherobject. The pose information that is tracked can be used to compensatefor the detected motion in data acquisitions for subsequent acquisitionsteps or slices or volumes within the same scan. Such embodiments can bedenoted “prospective motion correction” because the acquisition stepsare adapted prospectively during the scan to compensate for the motiondetected.

One important aspect of such embodiments of adapting imaging byprospective motion correction is the accuracy or resolution of themotion tracking system. Because of the high resolution generallyrequired for biomedical imaging, the motion tracking system in suchembodiments must also have a high resolution, because the motiontracking system's information will be used to align the variousacquisition steps. Accordingly, if the motion tracking system'sresolution is high enough, all of the acquisition steps can beaccurately aligned or registered despite a subject's motion. Conversely,if the motion tracking system's resolution is not high enough, theacquisition steps will not be accurately aligned or registered.

In some embodiments of adapting imaging by prospective motion correctionmagnetic resonance “navigator” signals can be utilized to estimate thepose of the subject and to dynamically correct for the subject's motion.Further, a magnetic resonance based navigator can also be utilized foradaptive motion correction in magnetic resonance imaging. In otherembodiments, small radiofrequency coils can be utilized to trackcatheters during interventional magnetic resonance imaging.

While such embodiments of magnetic resonance based adaptive magneticresonance imaging techniques provide good or satisfactory results inmany situations, they intrinsically interfere with the magneticresonance acquisition process. Further, such embodiments can work onlyfor a limited number of magnetic resonance sequences and can be limitedto measuring the position or pose of a subject a few times per second atbest.

Accordingly, in some embodiments, external or non-magnetic resonancebased techniques can be utilized to track subject motion rather thanmagnetic resonance based methods. For example, one or more opticalmethods can be utilized. In some embodiments, the pose information fromthe tracking system can be sent to the magnetic resonance scanner and beused by the scanner to compensate for the motion in subsequentacquisition steps.

In some embodiments, stereovision can be utilized to track the motion ofa subject, for example by using two or more cameras and multiple, atleast two markers. In other embodiments, accurate tracking of thesubject, for example the head or brain or other organ, can be achievedusing a single camera and a special marker in the magnetic resonanceenvironment. For example, the special marker can be a self-encodedmarker, a retrograde reflector or RGR or Moiré Phase Tracking target.Optical systems can provide accurate, non-contact sensing with a passiveand non-magnetic target and can also provide fast pose updates on theorder of 100 to 1,000 poses per second or even faster.

In some embodiments pose data from the tracking system are sent in nearreal time to a magnetic resonance scanner, which then nearlycontinuously updates scan parameters prior to each acquisition step orline in k-space. This way, the scan planes are locked relative to themoving object of interest. Images acquired with such embodiments ofprospective motion correction can show substantially reduced motionartifacts compared to images acquired without motion correction.

However, in some situations pose data as received by the magneticresonance scanner may be imperfect, for example due to inaccuracies ornoise in the tracking system or due to lag times between the markermovement and arrival of tracking data on the scanner. In order tocorrect for such inaccuracies or delays, some of these inaccuracies ordelays can be determined after the magnetic resonance scan has beenacquired in certain embodiments as the entire tracking data are thenavailable. More specifically, when prospective motion correction isapplied, subject motion between the pose detection and magneticresonance data acquisition can occur due to the time required to acquireand transfer marker images to the tracking computer, calculate poseinformation, perform magnetic resonance sequence updates, and theintrinsic timing of the sequence. Accordingly, differences between theassumed or estimated pose and the true pose during the acquisition stepmay cause residual motion artifacts. Similarly, inaccuracies in thetracking system, such as tracking noise, can cause errors. However, incertain embodiments some of these effects of tracking errors on magneticresonance signals can be corrected retrospectively within the datareconstruction by comparing the estimated or assumed pose from thetracking system and the true pose that is available after theacquisition step.

The shortcomings of such embodiments of non-magnetic resonancecorrection methods and others, however, are related to the fact thatsuch embodiments use updates of scan parameters once prior to eachmagnetic resonance acquisition step or line in k-space. In fact,magnetic resonance acquisitions involve a sequence of events. Forexample, a common sequence involves excitation of the spin system usingone or more radiofrequency pulses, possibly slice selective, spatialencoding using spatially variable switched magnetic fields (gradients),possible further manipulations of the spin system such as rephasing andcomplementary information encoding steps, and data acquisition. For somesequences, excitation may be preceded by an extra module to prepare thespin system to achieve a certain contrast. As a result, acquisition of asingle k-space line may last a few milliseconds to several hundredmilliseconds. However, pose updates for prospective motion correctionembodiments above have been applied immediately prior to excitation foreach individual magnetic resonance acquisition or k-space line.Consequently, pose updates may be applied approximately ten times persecond, even if the tracking system is capable of tracking at a higherrate, for example at 100 poses per second.

The scheme described above of updating scan parameters once perindividual acquisition step or k-space line can provide adequate motioncorrection if the object of interest does not move too fast. However, ifthe motion of the subject within an individual acquisition step becomestoo fast, then additional motion artifacts may be generated in theresulting images, which cannot be corrected with once per acquisitionpose updates. Such motion can be denoted “intra-scan motion.”

Accordingly, in some embodiments, motion artifacts due to substantialintra-scan motion can be eliminated or attenuated by attempting tonearly continuously update magnetic field gradients and radiofrequencypulses during each acquisition. This way their orientation is perfectlyaligned with the moving object of interest at any time. For example,such an embodiment can be implemented for diffusion-weighted magneticresonance imaging, which involves very strong magnetic field gradientsand is particularly sensitive to subject motion. In certain embodiments,a single magnetic resonance acquisition step, which typically involves asingle sequence block of approximately 100 milliseconds for itsapplication, can be broken down into multiple separate blocks, eachlasting approximately two milliseconds. The direction of gradients foreach of these two millisecond blocks can be updated using the mostrecent tracking data, resulting in a quasi-continuous pose update duringthe acquisition.

Despite the features of embodiments of quasi-continuously updatingparameters during each acquisition as described above, implementation ofsuch a quasi-continuous pose date scheme is extremely challenging andmay not be possible on all available magnetic resonance scannerplatforms. In addition, an ideal implementation of such embodiments ofquasi-continuous correction methods during each acquisition wouldnecessarily require that updates are made continuously. In contrast,current magnetic resonance scanners cannot update gradient orientationscontinuously. As such, pose updates can be applied onlyquasi-continuously, for example every two milliseconds. Consequently, itwould be advantageous to have a simpler scheme to correct for intra-scanmovements that does not rely on ideally continuous updates ofmeasurement parameters.

Intra-Scan Motion Correction—Introduction

As generally described above, movement by a subject during a magneticresonance scan can present significant problems in obtaining clearimages of the subject. The effects of motion of a subject during amagnetic resonance scan are illustrated in FIGS. 1A and 1B. FIG. 1Aillustrates the effects of a subject's motion during a magneticresonance scan by a conventional magnetic resonance scanner. Asillustrated in FIG. 1A, if a subject of a magnetic resonance imagingscan, such as a head, is titled to a certain degree, the resulting sliceor image from that scan, which is stationary, inevitably becomes tiltedrelative to the subject as well. Such movement by the subject during ascan can result in blurry and/or unclear images. As a result, theacquired magnetic resonance scan may not be useful to a medicalprofessional or the subject may be required to redo the entire magneticresonance scan, resulting in an unnecessary burden in time and cost.

However, by utilizing one or more intra-scan motion correction methodsdescribed herein, the geometry and/or phase of a signal can be updatedperiodically and/or prospectively during a scan to substantially matchthe motion of the subject. FIG. 1B illustrates the effects of a motionof a subject during a magnetic resonance scan by an intra-scan motioncorrection system. As illustrated in FIG. 1B, as the subject, or head inthis example, is tilted or moved, the slice plane of the magneticresonance scanner and/or phase and/or read orientations can also betilted and/or adjusted to account for the motion of the subject. Thisway, any or substantially all of the subject's movement can be accountedfor, resulting in a clean image that is substantially similar to animage that would have been acquired if the subject had not moved at all.Accordingly, by utilizing one or more methods, systems, and devices foran intra-scan motion correction as described herein, a subject of amagnetic resonance imaging scan can be allowed to move with attenuatedand/or without any such detrimental effects to the imaging results.

In general, slow motions of a subject during a magnetic resonance scancan be defined as movements with speeds of about 1 mm/sec or 1degrees/sec. Such slow motions can comprise slow drifts and can benearly imperceptible. Moderate motions of a subject during a magneticresonance scan can be defined as movements with speeds of about 10mm/sec or 10 degrees/sec. Such moderate motions are perceptible and canbe common in children and sick or confused patients. Fast motions of asubject during a magnetic resonance scan can be defined as movementswith speeds of about 100 mm/sec or 100 degrees/sec or faster. Such fastmotions can occur due to coughing or extreme agitation and can belimited in range and duration, for example 100 ms, due to confinedspace.

In some embodiments of methods, systems, and devices for intra-scanmotion correction as described herein, motion artifacts arising fromslow and moderate motions can be accounted for. In certain embodimentsof methods, systems, and devices for intra-scan motion correction asdescribed herein, even motion artifacts arising from fast motions canalso be accounted for.

In general, some effects of motion on moving spins can comprise unwantedphase shifts between excitation and signal readout, unwanted posechanges between phase-encoding steps (or lines in k-space), anduncorrected pose changes between successive slices or volumes.Uncorrected pose changes between successive slices or volumes can occurin ultra-fast acquisitions that image the entire subject or brain everyfew seconds. Such volumes can be translated and rotated. Unwanted posechanges between phase encoding steps can result in blurring; in otherwords, the object of interest can be imaged at variable poses. Lastly,unwanted phase shifts between excitation and signal readout can resultin artifacts in the phase-encoding direction after image reconstruction.The unwanted pose changes and uncorrected pose changes are purelygeometric and thus can relatively easily be corrected. However,correcting phase shifts can be more complicated.

Generally, the magnetic resonance scanner detects the sum ofmagnetization of the individual spins in a given volume. The sum ofsignals from all individual spins is detected. In order for the magneticresonance signal to be detectable, phases of individual spins need to becoherent or aligned. Loss of phase coherence of spins can cause signalattenuation or loss. In order to ensure phase coherence during signaldetection, gradients have to be balanced throughout a pulse sequence,because gradients affect a spin's frequency and phase dependent on thespin's spatial position. Furthermore, the phase of the signals detectedhas to be aligned across acquisition steps or lines in k-space. However,motion interferes with this process by inducing unintended phase shifts.Accordingly, motion artifacts caused by phase shifts can be corrected ifthe phase shifts can be accounted for.

In order to account for a subject's motion during a magnetic resonancescan the motion of the object of interest can first be characterizedmathematically. The object of interest can be assumed for example to bea rigid body. Mathematically, the pose of the object can becharacterized by six time dependent parameters, three translations andthree rotations. In other words, a pose of an object can be consideredto comprise six degrees of freedom. In contrast, orientation of anobject can comprise two or more degrees of freedom, three or moredegrees of freedom, four or more degrees of freedom, or five or moredegrees of freedom.

The 3 translations can form a translation vector X(t) and the 3rotations can form a rotation matrix R(t), where t represents time. Thetrajectory of a spin (initial vector position x₀) inside the imagingvolume can then described by the vector equation: x(t)=X(t)+R(t)·x₀.

As described above, a magnetic resonance sequence generally involves aseries of radiofrequency pulses, switched magnetic field gradients, andone or more acquisition events. For simplicity, a sequence involving asingle excitation radiofrequency pulse (at time t=0), followed by a timeseries of gradients [denoted by vector G(t)] and data acquisition can beconsidered. Motion within this sequence (“intra-scan motion”) altersboth the zero-order phase (due to translations) and effective gradientmoment M (due to rotations) in the object coordinate system.

Translations X(t) will cause a change in the overall phase φ of theobject at the time T of data acquisition, and rotations R(t) will causea change in the gradient moment M of the object at the time T of dataacquisition. It can be shown that the effects of translations androtations are as follows:

$\begin{matrix}{M = {\int_{0}^{T}{{R^{- 1}(t)} \cdot {G(t)} \cdot {dt}}}} & (1) \\{\phi = {2{\pi \cdot \gamma}{\int_{0}^{T}{{X(t)} \cdot {G(t)} \cdot {dt}}}}} & (2)\end{matrix}$

where time t=0 denotes excitation of the spin system and y is thegyromagnetic ratio. For a stationary object (R(t)=1), equation 1 reducesto:

M_(stationary) = ∫₀^(T)G(t) ⋅ dt = 0

which equals zero since magnetic resonance sequences are generallybalanced (first gradient moment between excitation and data acquisitionis zero). However, time-dependent rotations induce a gradient imbalance(residual gradient moment M as per Eq. 1) that can result in signalattenuation or dropouts in the presence of sufficiently strong motion.Additionally, since gradient moments are used for spatial encoding,motion-dependent alterations in gradient moments can alter the spatialencoding of magnetic resonance signals and cause artifacts during imagereconstruction. Likewise, time dependent translations can induce aspatially constant phase as per Eq. 2 that can vary from one acquisitionstep to another and can lead to artifacts in the reconstructed data.

These phase and gradient moment effects caused by intra-scan motionarise from the interaction between the moving object and switchedmagnetic field gradients. However, most embodiments of non-continuousmotion correction methods consider only geometric effects of motion,such as ensuring that scan planes are aligned correctly during scans(see, for example, FIG. 1B), with the exception of the quasi-continuousembodiment described above. However, the geometric effects andphase/gradient moment effects are conceptually entirely different. Forinstance, phase effects may occur even if all geometric effects arecorrected, and vice versa. Accordingly, in order to accurately correctfor movement and/or motion of a subject during a magnetic resonancescan, both geometric effects and phase/gradient moment effects must beaccounted for.

FIG. 2 illustrates the phase/gradient movement effects in generating amagnetic resonance image via k-space when the subject moves inorientation and/or pose. When a subject of a magnetic resonance scanremains completely still and does not move, the data acquired from suchscan is generally placed in the correct position of k-space which isdenoted by the intersection between the center vertical line and one ormore solid horizontal lines as depicted in FIG. 2. However, when thesubject of a magnetic resonance scan moves, the data acquired cannot beplaced in the correct k-space either vertically and/or horizontally.Vertical displacement, or placing an acquired data off of a horizontalparallel line, denotes an error in the phase encoding. Horizontaldisplacement, or placing an acquired data off of the center verticalline, denotes an error in the read encoding or frequency encoding. Inother words, the x axis in k-space is encoded by a read gradient, andthe y axis in k-space is encoded by a phase gradient. As such, the phaseencoding gradient, or the read encoding gradient, or both the phaseencoding gradient and the read encoding gradient must be updatedaccording to the detected motion of the subject in order to account forsubstantially all motion effects by the subject during the scan.Further, rotations in space generally correspond to rotations ink-space. Therefore, rotations of the subject may be corrected byadjusting phase encoding gradients and/or frequency encoding gradientsso that they match the rotation of the subject to be scanned. In someembodiments, translations of the subject can essentially be approximatedby phase shifts that vary linearly in k-space and corrected forintra-scan or during image reconstruction.

Intra-Scan Motion Correction—System Overview

As described above because both geometric and phase/gradient movementeffects must be accounted for in order to better correct motion of asubject during a magnetic resonance scan, embodiments of the intra-scanmotion correction systems, methods, and devices described hereincomprise one or more techniques of targeting these effects. Also,embodiments of the intra-scan motion correction systems, devices, andmethods described herein generally use less data processing capabilitiescompared to the quasi-continuous embodiment described above and can beutilized with the majority of currently available magnetic resonancescanners. Additionally, prospective update errors due to the inherentlag time, noise, or the like in the quasi-continuous correctionembodiment described above can be eliminated in embodiments of theintra-scan motion correction system, methods, and devices describedherein.

FIG. 3 illustrates an embodiment of a system for intra-scan motioncorrection. An intra-scan motion correction system can be configured tobe used in conjunction with one or more magnetic resonance scanners. Insome embodiments, a magnetic resonance scanner can comprise anintra-scan motion correction system. In other embodiments, a magneticresonance scanner and an intra-scan motion correction system arephysically separate. In certain embodiments, one or more parts ormodules of a magnetic resonance scanner and an intra-scan motioncorrection system are shared and/or accessible by the other.

As illustrated in FIG. 3, an embodiment of an intra-scan motioncorrection system can generally comprise a main computing system 300, auser interface 302, and a display for outputting constructed images 334.In some embodiments, the user interface 302 can allow a medicalprofessional and/or other user to control the intra-scan motioncorrection system and/or magnetic resonance system, such as turning thesystem on or off and/or controlling one or more parameters of thesystem. By utilizing the user interface 302, a user can instruct themain computing system 300 to turn a magnetic field gradient 304 on oroff by transmitting the instruction from the main computing system 300to a magnetic field gradient generator 304. In addition a user can usethe user interface 302 to instruct the main computing system 300 to turna radiofrequency signal generator 306 on or off and also control theradiofrequency signal generator 306 to emit a radiofrequency signal of acertain type.

The motion tracking system 310 can track substantially any and allmotion of the subject 308 during a magnetic resonance imaging scan. Themotion tracking system 310 can comprise any of the motion trackingsystems that are currently known or to be developed in the future. Forexample, the motion tracking system 310 can be an optical orstereovision system (in-bore or out-bore), optical system with multiplecameras (in-bore or out-bore), laser-based tracking system with orwithout a reflector (in-bore or out-bore), radiofrequency pickupcoils-based system (in-bore), magnetic field gradient monitoring system(in-bore), wire loop recordings-based system (for example, using EEGequipment), self-encoded marker-based system, single camera-based system(in-bore or out-bore), mechanical detection system, magnetic fieldgradient monitoring-based system, ultrasound-based system, or the like.After the motion tracking system 310 tracks the motion of the subject308, the tracking data can be transmitted from the motion trackingsystem 310 to the main computing system 300. In some embodiments, themotion tracking system 310 is configured to track and/or send datarelated to the motion of the subject 308 in real time.

In some embodiments the motion tracking data that is collected by themotion tracking system 310 is transmitted to the main computing system300 over a computer network periodically in packets of data. In otherembodiments the motion tracking data collected by the motion trackingsystem 310 is transmitted over a computer network to the main computingsystem 300 at once in a relatively large data packet.

The magnetic field gradient and/or radiofrequency signals that aregenerated by the magnetic field gradient generator 304 andradiofrequency signal generator 306 respectively can affect themagnetization of one or more nuclei of the subject 308. By manipulatingthe magnetic field gradient and radiofrequency signal, such generatedmagnetization can be further manipulated in the subject 308, resultingin a signal emission from the subject 308. The emitted signal can bedetected by one or more magnetic resonance detector devices and/orreceivers 312. Such detected data by the magnetic resonance detectordevice and/or receiver can be transmitted over a computer network oranother connection to the main computing system 300.

The data transmitted from the motion tracking system 310 to the maincomputing system 300 can be further processed by the motion trackingmodule 314. For example, the motion tracking module 314 can beconfigured to generate a motion trajectory of the subject 308. Any suchmotion data that is transmitted from the motion tracking system 310and/or motion data that is further processed by the motion trackingmodule 314 can be stored in a database 332 of the main computing system300.

Based on the detected motion data by the motion tracking system 310, ageometry update module 316 can be configured to update and/or adjust oneor more geometric parameters accordingly in order to compensate for thesubject's motion. Any or all geometric parameter updates by the geometryupdate module 316 can further be stored in the database 332 of the maincomputing system 300.

Further, based on the detected motion data by the motion tracking system310, a phase encoding update module 318 can be configured to update oneor more phase encoding gradients. The phase encoding gradient updatesthat are processed by the phase encoding update module 318 can furtherbe stored in the database 332 of the main computing system 300.

In addition, a read encoding gradient update module 320 can beconfigured to update one or more read encoding gradients based on themotion of the subject 308 as detected by the motion tracking system 310.The read encoding gradient updates that are processed by the readencoding update module 320 can further be stored in the database 332 ofthe main computing system 300.

The main computing system 300 can further comprise a magnetic resonancesequence module 324. The magnetic resonance sequence module 324 can beconfigured to process a particular magnetic resonance sequence or aseries thereof for one or more magnetic resonance scans. The processedmagnetic resonance sequence can be generated by the magnetic fieldgradient generator and/or radiofrequency signal generator 306 andapplied to a subject 308. The magnetic resonance sequence module 324 canfurther be configured to track or log one or more magnetic resonancesequences, which can then be stored in the database 332 of the maincomputing system 300.

Further, a correction gradient calculation module 326 of the maincomputing system 300 can be configured to calculate a first gradientmoment during one or more magnetic resonance scans. More specifically,in certain embodiments, the correction gradient calculation module 326is configured to calculate the (first) gradient moment according toEquation 1 and using the tracked pose and/or orientation data and agradient signal and/or sequence used during one or more scans. The(first) gradient moment is the time integral of the gradient waveform.In other words, the (first) gradient moment is the area beneath thegradient waveform when plotted against time. In certain embodiments, thegradient waveform can be triangular, trapezoidal, sinusoidal or the likein shape. In other certain embodiments, the gradient waveform may be asuperposition of a non-corrected gradient waveform with a triangular,trapezoidal, sinusoidal, waveform or the like in shape. In someembodiments, the only property of the gradient waveform that is requiredin a method for intra-scan motion correction is the first gradientmoment according to Equation 1.

As discussed above, it is a motion-induced alteration in this gradientmoment that can cause phase-based motion artifacts in magnetic resonancescans. Accordingly, in some embodiments, a correction gradient or a“blip” gradient can be applied to the subject 308 in order to counteractand/or reverse the effects of the altered first gradient moment. Assuch, in certain embodiments, the correction gradient calculation module326 is further configured to determine an appropriate correctiongradient moment to be applied to the subject 308. The appropriatecorrection gradient moment can be equal to the first gradient moment inabsolute value but with an opposite sign from the first gradient momentaccording to Equation 1. In other words, by applying a correctiongradient with a moment of −M, motion artifacts caused by a gradientmoment of M can be accounted for and the signal phase can be corrected.

In certain embodiments, a correction gradient of a moment as determinedby the correction gradient calculation module 326 can be applied to asubject 308 by a magnetic field gradient generator 304. Further, in someembodiments, the (first) gradient moment and/or correction gradientmoment that is calculated can be stored in a database 332 of the maincomputing system 300.

In some embodiments, a phase correction module 328 can be configured tocorrect errors in one or more constant phases due to subject motion(according to equation 2) prior to data acquisition, during dataacquisition, and/or during the reconstruction process of the image. Incertain embodiments, the phase correction module 328 is configured tocorrect errors based on the tracked pose data and/or Equation 2. Thephase corrections that are processed by the phase correction module 328can further be stored in the database 332 of the main computing system300.

Additionally, the main computing system 300 can also comprise an errorcorrection module 330. The error correction module 330 can be configuredto identify and correct any residual errors that remain after dataacquisition. For example, the error correction module 330 can beconfigured to identify and/or correct errors in orientation, pose,and/or phase. In some embodiments, the error correction module 330 canbe configured to correct one or more residual errors in one or moregeometry parameters and/or signal phase and/or first gradient momentthat are present after applying or without applying one or more geometryupdates, phase encoding updates, read encoding gradient updates, and/orapplication of an additional magnetic moment correction gradient. Forexample, the error correction module 330 can be configured toretrospectively correct errors in one or more geometry parameters,gradient moment, and/or phase.

In certain embodiments, the error correction module 330 can beconfigured to correct for one or more errors due to lag time inobtaining and processing orientation and/or pose data, noise in data, orthe like. For example, due to such lag time and/or noise, errors mayexist in one or more geometry updates, phase encoding gradient updates,read encoding gradient updates, and/or calculation of a correctiongradient, because all such calculations are based in part on the trackedpose and/or orientation data. Because the true pose and/or orientationdata are available after data acquisition or a scan is complete, suchdiscrepancies due to lag time or noise can be resolved. Further, anysuch residual errors that are corrected by the correction module 330 canfurther be stored in a database 332 of the main computing system 300.

The main computing system 300 can further comprise an image constructionmodule 322. The image construction module 322 can be configured toconstruct and/or reconstruct an image based on the one or more signalsemitted from the subject 308. In some embodiments, the imageconstruction module 322 can further be configured to construct and/orreconstruct an image based in part on data that is processed by themagnetic resonance imaging sequence module 324, the geometry updatemodule 316, phase encoding update module 318, read encoding gradientupdate module 320, correction gradient calculation module 326, and/orthe correction module 330.

An image that is constructed and/or reconstructed by the imageconstruction module 322 can further be transmitted over a computernetwork or other connection to one or more displays for outputting aconstructed image 334. A user and/or medical professional can view theconstructed image via the display for outputting the constructed image334.

Intra-Scan Motion Correction—Method Overview

Systems, methods, and devices for intra-scan motion correctioncompensate not only from one line or acquisition step to the next, butalso within each acquisition step or line in k-space.

FIG. 4 is a time frame diagram that illustrates the time frame of one ormore methods for an intra-scan motion correction. In some embodiments, amethod for an intra-scan motion correction can comprise one or moreblocks, including but not limited to an update geometry parametersblock, an update phase and/or read encoding gradient(s) block, an applycorrection gradient block, and/or an error correction block or anysub-blocks thereof. Additionally, a method for intra-scan motioncorrection can comprise a phase correction block. Further, a method forintra-scan motion correction can comprise any selective combination ofthese blocks and/or more specific blocks thereof.

In some embodiments, the update geometry parameters block, update phaseand/or read encoding gradient(s) block, apply correction gradient block,and apply phase correction block, can be applied on a magnetic resonancescanner in near real-time. In certain embodiments, the error correctionblock can be applied after data acquisition during image reconstruction.However, other implementations are possible as well.

In some embodiments, an update geometry parameters block can compriseupdating a prospective slice and/or geometry 402. The prospective sliceand/or geometry update can occur immediately before one or moreradiofrequency pulses. For example, a prospective slice and/or geometryupdate can occur prior to and/or immediately prior to excitation via aninitial radiofrequency pulse. The prospective slice and/or geometryupdate can also occur prior to and/or immediately prior to an optionalinitial magnetic gradient field. In addition, a prospective slice and/orgeometry update can occur prior to and/or immediately prior to anyadditional radiofrequency pulses and/or optional magnetic gradientfields. In certain embodiments, there can be one or more additionalradiofrequency pulses and/or optional magnetic gradient fields. In otherembodiments, there are no additional radiofrequency pulses and/oroptional magnetic gradient fields.

In some embodiments an update phase and/or read encoding gradients blockcan comprise prospectively updating the orientation or pose of a phaseencoding gradient and/or a frequency (read) encoding gradient. Theprospective phase encoding gradient update can occur at any time betweenexcitation and data acquisition 410. For example in some embodiments, aprospective phase encoding gradient update 404 can occur immediatelyafter excitation and/or an optional magnetic gradient field. In certainembodiments, a prospective phase encoding gradient update 404 can occurat a time after excitation and/or optional magnetic gradient field. Incertain embodiments, a prospective phase encoding gradient update 404can occur in connection with an additional radiofrequency pulse and/oroptional magnetic gradient field. In certain embodiments, a prospectivephase encoding gradient 404 can occur concurrently with and/or inconjunction with a data acquisition process 410.

In some embodiments, a prospective frequency encoding gradient update406 can begin prior to and/or immediately prior to a data acquisitionprocess 410. In certain embodiments, a prospective frequency encodinggradient update 406 can occur concurrently with and in conjunction witha data acquisition process 410. In certain embodiments, a prospectivefrequency encoding gradient update 406 can end immediately prior to theend of a data acquisition process 410.

An apply correction gradient block can comprise applying a briefadditional gradient 408 to the subject to correct for a first gradientmoment as discussed above. In certain embodiments the correctiongradient 408 can be applied after excitation and/or optional magneticgradient fields and any additional radiofrequency pulses and/or optionalmagnetic gradient fields. In certain embodiments, the correctiongradient 408 can be applied to the subject immediately prior to dataacquisition 410. In certain embodiments, the correction gradient 408 canbe applied to the subject concurrently with any other magnetic fieldgradient.

Further, an apply phase correction block can comprise setting the phaseof the MR detector or receiver, or the phase of the data acquisition 410device to correct for zero-order phase errors 409 as determined byEquation 2. In certain embodiments, the phase correction block can beapplied to the subject immediately prior to or concurrent with dataacquisition 410.

In some embodiments an error correction block can comprise correctingany residual error 412 after data acquisition. In some embodiments,residual errors in one or more geometry parameters, phase, and/orgradient moments are corrected in the error correction block. Sucherrors can be present after applying or without applying one or moregeometry updates, phase encoding updates, read encoding gradientupdates, phase corrections and/or application of an additionalcorrection gradient.

In certain embodiments, residual errors can remain after processing themagnetic resonance data, with or without the update geometry parametersblock, update phase and/or read encoding gradients block, and/or applycorrection gradient block. In certain embodiments the error correction412 can occur after and/or immediately after data acquisition 410.

In some embodiments after the error correction block the system isconfigured to construct and/or reconstruct an image of the subject 414.In certain embodiments the system can be configured to reconstruct theimage based on the magnetic resonance data as inputted into k-space. Insome embodiments, the system is configured to reconstruct an imagefurther based on prospectively updated slices, phase encoding gradientupdates, frequency encoding gradient updates, application of acorrection gradient, and/or error correction.

Update Geometry Parameters Block

In some embodiments, one or more geometry parameters are updatedprospectively. For example, one or more geometry parameters can beupdated after excitation but before data acquisition. By prospectivelyupdating one or more geometric parameters rather than after dataacquisition, data processing time can be saved and a more isotropic,rectangular coverage of k-space can be obtained. If the one or moregeometric parameters are updated only retrospectively after dataacquisition, certain areas in k-space can be denser than others,possibly resulting in image artifacts and/or more complexreconstruction. Further, if the one or more geometric parameters areupdated only retrospectively after data acquisition, certain signals maybe attenuated or lost, and cannot be recovered during imagereconstruction.

FIG. 5 illustrates a process flow of an example of embodiments of one ormore methods of intra-scan motion correction during a magnetic resonancescan. In some embodiments, the update geometry parameters block can beapplied alone or in conjunction with one or more of an update phaseand/or read encoding gradient(s) block, apply correction gradient block,apply correction phase block, and/or error correction block orsub-blocks thereof.

In some embodiments, the orientation and/or pose of a subject is trackedvia one or more motion detectors at block 502. Based on the trackedorientation and/or pose of the subject the system can be configured toprospectively update one or more geometric parameters and/or sliceplanes at block 504. The one or more geometric parameters can compriseone or more parameters discussed above, including but not limited totranslation and rotation. As discussed, the prospective update ofgeometric parameters and/or slice planes 504 can occur prior to and/orimmediately prior to excitation of the spin system by applying aninitial radiofrequency pulse at block 506. Further, the excitation canoccur in conjunction with an optional magnetic field gradient at block506.

Subsequent prospective updates of geometric parameters and/or sliceplanes can occur at block 508. As discussed, any of one or more, if any,subsequent prospective updates of geometric parameters and/or sliceplanes 508 can occur prior to and/or immediately prior to applyingadditional radiofrequency pulses at block 510. The radiofrequency pulsescan be slice-selective refocusing, and/or slice-selective saturationand/or inversion pulses among others. The additional radiofrequencypulses can also be applied in conjunction with, before, and/or afterapplying an optional magnetic field gradient at block 510.

By updating the geometry parameters and/or slice planes immediatelyprior to all radiofrequency pulses, a line-by-line correction of motionbetween successive excitations is possible. In other words, signalsthroughout the entire measurement can be aligned in position.

In some embodiments, the system can be configured to conduct dataacquisition at block 512 based on the scanned magnetic resonance data.

Update Phase and/or Read Encoding Gradient(s) Block

As discussed, motion of a subject during a magnetic resonance scan canalso affect the orientation of phase/read encoding gradient, therebyresulting in motion artifacts. As such, in some embodiments, theorientations of phase and/or read encoding gradients are prospectivelyupdated. By prospectively updating the orientation of phase and/or readencoding gradients rather than after data acquisition, data processingtime can be saved and a more isotropic, rectangular grid in k-space canbe obtained. In other words, a more homogeneous coverage in density ink-space is possible. If the phase and/or read encoding gradients areupdated only retrospectively after data acquisition, certain areas ink-space can be denser than others, possibly resulting in more complexreconstruction and/or in image artifacts. Further, if the phase and/orread encoding gradients are updated only retrospectively after dataacquisition, certain signals may be encoded incorrectly, and cannot berecovered during image reconstruction.

FIG. 6 illustrates an example of an embodiment of an update phase and/orread encoding gradient(s) block of an embodiment of a method ofintra-scan motion correction during a magnetic resonance scan. In someembodiments, the update phase and/or read encoding gradient(s) block canbe applied alone or in conjunction with one or more of an updategeometry parameters block, apply correction gradient block, applycorrection phase block, and/or error correction block or sub-blocksthereof.

In some embodiments, at block 602, one or more motion detectors areconfigured to track the orientation and/or pose of the subject during amagnetic resonance scan. In some embodiments, the system can further beconfigured to apply excitation of the spin system at block 604 byapplying a radiofrequency pulse. In certain embodiments excitation ofthe spin system can occur in conjunction with, before, and/or afterapplying an optional magnetic field gradient at block 604.

As discussed, the orientation of a phase encoding gradient can beupdated at any time after excitation and/or in conjunction with dataacquisition 614. Prospectively updating the orientation of read encodinggradient and/or phase encoding gradient can occur at one or more of theblocks depicted in FIG. 6. Accordingly, in some embodiments, a phaseencoding gradient can be prospectively updated at block 606 afterexcitation of the spin system at block 604. However, a prospectiveupdate of the phase encoding gradient need not occur at this time.Alternatively, a prospective update of the phase encoding gradient canoccur at block 610 after applying one or more additional radiofrequencypulses at block 608. As discussed, any additional radiofrequency pulsescan be applied at block 608 in conjunction with, before, and/or afterapplying an optional magnetic field gradient.

Further, a prospective update of the orientation of read encodinggradient can occur at block 612 immediately prior to data acquisition atblock 614. In certain embodiments, the read encoding gradient can beupdated at block 616 in conjunction with data acquisition at block 614.In certain embodiments, the read encoding gradient can be updatedimmediately prior to data acquisition 614 at block 612 and repeatedly inconjunction with data acquisition 614 at block 616. Also, the phaseencoding gradient can also be updated in conjunction with dataacquisition 614 at block 618.

Apply Correction Gradient Block

If a subject of a magnetic resonance scan remains completely still anddoes not move during the scan, the first gradient moment over the scanshould ideally equal zero for a balanced magnetic resonance sequence.However, if a subject of a magnetic resonance scan moves even slightly,the first gradient moment after completion of the scan does not equalzero. The transverse magnetization generated by the excitation pulse isaffected by motion that occurs in the presence of gradients. Such motionaffects the phase of the magnetization and thus the first order gradientmoment depending on the direction and velocity of motion, and thedirection and sequence of the gradients applied.

As noted, motion affects the gradient moment/position of “lines” ink-space. If the movement is known or predicted, then the gradient momenteffects can be calculated as per Equation 1. Gradient moment alterationscan be compensated for by the application of additional brief gradientpulses prior to signal detection. Importantly, this type of motioncompensation with correction gradients is applicable for rotations.

Of note, many preparation RF pulses act on longitudinal magnetization tomodify the image contrast. Because longitudinal magnetization is notaffected by gradients, it can be unnecessary to apply correctioncompensation gradients in this instance. In other words, simplycorrecting the geometry via one or more sub-blocks of the updategeometry parameters block may be sufficient.

FIG. 7 illustrates an example of an embodiment of an apply correctiongradient block of an embodiment of a method of intra-scan motioncorrection during a magnetic resonance scan. In some embodiments, theapply correction gradient block can be applied alone or in conjunctionwith one or more of an update geometry parameters block, update phaseand/or read encoding gradient(s) block, apply correction phase block,and/or error correction block or sub-blocks thereof.

As illustrated in FIG. 7, the system can be configured to track theorientation and/or pose of a subject during the scan via one or moremotion detectors at block 702. In some embodiments, the spin system isexcited by applying an initial radiofrequency pulse at block 704.Further, as discussed, in certain embodiments, the excitation can beapplied in conjunction with one or more optional magnetic fieldgradients at block 704. In other embodiments, the system can beconfigured to apply additional magnetic field gradients. Such magneticfield gradients can comprise, for example, diffusion weightinggradients, flow encoding gradients, elasticity encoding gradients,gradients to eliminate unwanted spin coherences called spoiler orcrusher gradients, gradients to prewind or rewind gradient moments,and/or other gradients. Additionally, one or more additionalradiofrequency pulses can be applied to the subject at block 706. Theseone or more additional radiofrequency pulses can also be applied inconjunction with, before, and/or after applying one or more optionalmagnetic field gradients at block 706.

Apply Phase Correction Block

Further, if a subject of a magnetic resonance scan moves even slightly,the phase of the signal is altered. The transverse magnetizationgenerated by the excitation pulse is affected by motion that occurs inthe presence of gradients. Such motion affects the phase of themagnetization depending on the direction and velocity of motion, and thedirection and sequence of the gradients applied.

Motion affects both the phase of the signals acquired, as well as thegradient moment/position of “lines” in k-space. If the movement is knownor predicted, then the phase effect can be calculated as per Equation 2.Phase alterations as per equation 2 may be compensated for by acquiringdata at the correct reference-phase.

Accordingly, in some embodiments, a method of intra-scan motioncorrection comprises an apply correction phase block. FIG. 7Aillustrates an example of an embodiment of an apply correction phaseblock of an embodiment of a method of intra-scan motion correctionduring a magnetic resonance scan. In some embodiments, the apply phasegradient block can be applied alone or in conjunction with one or moreof an update geometry parameters block, update phase and/or readencoding gradient(s) block, apply gradient correction block, and/orerror correction block or sub-blocks thereof.

In some embodiments the apply correction phase block can comprisecalculating the correction phase at block 720. More specifically,Equation 2 and the tracked pose can be utilized to calculate thecorrection phase. The calculated correction phase can be applied tocompensate for any or all phase effects at block 722. Further, thesystem can be configured to conduct data acquisition at block 724 afterapplying the correction gradient block in some embodiments.

Error Correction Block

In some situations, error can be present after data acquisition. Forexample, in some embodiments where the geometry, phase, and/or readencoding gradients are not updated prospectively or if a correctiongradient is not applied, phase/gradient error and orientation error canbe present in the data acquired. In certain embodiments, even afterapplying one or more of an update geometry parameters block, updatephase and/or read encoding gradient(s) block, apply correction phaseblock, and/or apply correction gradient block, residual error in thephase/gradient and/or orientation can still be present. For example, theprospective update blocks are based on packets of orientation and/orpose data that are transmitted periodically from one or motion detectorsto the computing system. However, there is an inherent lag time involvedin the transmittal and processing of this data. Accordingly, one or moreerrors can still remain after prospective update blocks. As such, insome embodiments, an error correction block is applied toretrospectively correct for any remaining error.

FIG. 8 is a process flow diagram illustrating an error correction block.In some embodiments, the error correction block can be applied alone orin conjunction with one or more of an update geometry parameters block,update phase and/or read encoding gradient(s) block, apply correctionphase block, and/or apply correction gradient block or sub-blocksthereof.

In some embodiments, a system can be configured to track the orientationand/or pose of a subject during a magnetic resonance imaging scan viaone or more motion detectors at block 802. In certain embodiments, thespin system can be excited by applying an initial radiofrequency pulseat block 804. The excitation, in certain embodiments, can be applied inconjunction with applying an optional magnetic field gradient at block804. In some embodiments the system can be configured to apply one ormore additional radiofrequency pulses at block 806. The one or moreadditional radiofrequency pulses can also be applied in conjunctionwith, before, and/or after one or more magnetic field gradients. Themagnetic resonance scan data can be collected at block 808 by the systemin some embodiments.

Any residual errors that are present after data acquisition 808 can bedetermined by the system and/or corrected during an error correctionblock. For example, any residual errors in one or more geometryparameters and/or phase or gradient moment that are present afterapplying or without applying one or more geometry updates, phaseencoding updates, read encoding gradient updates, and/or application ofan additional correction gradient can be corrected.

In certain embodiment, the system can be configured to determinediscrepancies between predicted motion, from the orientation and/or posedata that was collected and transmitted periodically to the system atblock 802, and the actual motion data at block 810. The actual motiondata, in certain embodiments, can only be determined after the dataacquisition process is complete.

As discussed above, errors in the predicted motion from the orientationand/or pose data that is periodically detected and sent to the system atblock 802 can comprise one or more errors due to the inherent lag timeand/or noise. Because of such potential errors in the predicted motiondata, there can also be some residual errors in orientation and/or poseor phase/gradient even after applying one or more of an update geometryparameters block, update phase and/or read encoding gradient(s) block,apply correction gradient block, apply correction phase block, and/orsub-blocks thereof. Such residual errors can be corrected during theerror correction block based on the determined discrepancies between thepredicted motion and actual motion.

Further, small errors in the orientation of phase and read-encodinggradients can also be corrected during reconstruction, for instance, byinterpolating the originally acquired raw data to a rectilinear raw datagrid prior to Fourier transformation.

In some embodiments, the system can be configured to reconstruct animage based on the magnetic resonance scan, orientation and/or poseupdate, phase encoding gradient update, read gradient update,application of correction gradient, apply correction phase block, and/orany errors corrected during the error correction block at block 814.

Motion Effects—Examples

FIG. 9 is a schematic diagram illustrating the effects of an embodimentof a method of intra-scan motion correction during a magnetic resonancescan. The illustrated embodiment in FIG. 9 comprises prospectivelyupdating one or more geometry parameters, prospectively updating phaseand/or read gradient(s), and applying a correction gradient.

As discussed above, in some embodiments, one or more slice updates orgeometric updates are applied prior to and/or immediately prior to oneor more radiofrequency pulses, including but not limited to excitationof the spin system. RF1 through RF3 correspond to one or moreradiofrequency pulses. As illustrated, a slice update can occurimmediately prior to application of radiofrequency pulse RF1. Further,another slice update can occur immediately prior to anotherradiofrequency pulse RF2. Additionally, another slice update can occurimmediately prior to applying another radiofrequency pulse RF3.

P1 through P7 correspond to individual periodic packets of orientationand/or pose data that is detected by one or more motion detectors andtransmitted to the magnetic resonance system in some embodiments. Asillustrated, one or more slice updates can be applied by the systemusing the orientation and/or pose data packet that was transmitted tothe system immediately prior to one or more slice updates and/orgeometric updates. For example, a first slice update can be appliedbased on data packet P1. Further, another slice update can be appliedbased on the orientation and/or pose data packet P2. Additionally,another slice update can occur using the orientation and/or pose datapacket P6.

In contrast to some embodiments where motion of a subject betweenexcitation, for example RF1, and data acquisition, AQ, is ignored asnegligible, the depicted embodiment prospectively updates geometricparameters within a single magnetic resonance scanning step to obtainclearer images. The second horizontal line denoted SL corresponds toslice gradients and updates. As illustrated in FIG. 9, the one or moreslice updates are applied immediately prior to one or moreradiofrequency pulses using an orientation and/or pose data packet thatwas received immediately prior to the slice update.

The third horizontal line denoted PH corresponds to phase encodingdirection. As illustrated in FIG. 9, the phase encoding gradient in someembodiments is updated immediately prior to data acquisition, which islabeled AQ. In some embodiments, the data acquisition can last foranywhere from about one milliseconds to about 100 milliseconds orlonger.

The fourth horizontal line denoted RO corresponds to the readoutdirection. As illustrated in FIG. 9, in some embodiments the readencoding update is applied immediately prior to or concurrently withdata acquisition. In some embodiments, read encoding update is notrequired. Rather, only phase encoding update and/or geometry update isapplied.

G1 through G4 in the PH horizontal line correspond to additionalmagnetic field gradients used to encode additional information, such asmicroscopic diffusion of molecules, or to eliminate unwanted signals, orfor other purposes. As discussed above, if a subject does not move andremains completely still during a magnetic resonance scan, there is nogradient moment build-up. In other words, the sum of the areas of G1-G4should equal zero. However, if the subject moves during a magneticresonance scan, the interaction of gradients G1 through G4 with themoving subject causes the gradient moment build-up to not equal zero.This gradient moment build-up can cause additional motion artifacts inthe scanned image.

Accordingly, in some embodiments, the system is configured to apply anadditional brief gradient or a correction gradient to reverse theeffects of the total gradient moment. In some embodiments, thecorrection gradient is simply the inverse of the gradient momentbuild-up. In the depicted embodiment, a “blip” or a correction gradientmoment is calculated prior to or immediately prior to data acquisition.As illustrated, in order to calculate the gradient moment build-up,which is the integral of the gradient sequence multiplied by therotation matrix during the scan, orientation and/or pose data packetsfrom the entire scan duration can be used. For example, in the depictedembodiment, P1-P7 can be used in conjunction with the gradient sequenceto calculate the gradient moment build-up.

However, as discussed, lag time and/or noise may be present in theorientation and/or pose data packets. For example, it requires time fordata packet P5 to be transmitted from one or more motion detectors tothe computer system and to be processed. As a result, such lag timeand/or noise in orientation and/or pose data leads to possible errors inthe prospective updates to one or more geometry parameters,phase/gradient, and/or calculation of a correction gradient.

However, after data acquisition, in some embodiments, the one or moremotion detectors can be configured to continue to collect orientationand/or pose data, for example P8 and/or P9. With such continued data,the lag time can be accounted for. For example, each data packet can beshifted in time by a certain amount in order to account for the lagtime. By shifting the time of orientation and/or pose data, the systemcan obtain true orientation and/or pose data and determine and/orcorrect any errors remaining after data acquisition.

FIG. 10 is another schematic diagram illustrating the effects of anembodiment of a method of intra-scan motion correction during a magneticresonance scan. In FIG. 10, the first horizontal line RF illustrates theradiofrequency sequences. G_(SL), G_(PE), and G_(RO) represent slicegradient, phase encoding gradient, and readout gradient respectively.

The echo time (TE) corresponds to the time between the center orexcitation and the center of data acquisition. Similar to FIG. 9, aslice update is conducted by the system immediately prior to excitation.Further, a phase encoding gradient update is conducted by the systembetween excitation and data acquisition. Additionally, a correctiongradient is applied by the system to the subject before dataacquisition. The correction gradient in FIG. 10 is illustrated by thepulses located within the oval. Moreover, a read encoding gradientupdate can be conducted by the system in conjunction with dataacquisition. For example, a read encoding gradient update process canbegin immediately prior to data acquisition and continue to be conductedthroughout the data acquisition process.

Further, in FIG. 10, another slice update is applied immediately beforeexcitation of a second magnetic resonance scan. Repetition time (TR)refers to the time between the excitation of a first scan and a secondscan.

As discussed, many embodiments of non-intrascan motion correctionsystems update scan parameters only once prior to each “excitation”radiofrequency (RF) pulse, which is typically every 100 ms or lessfrequently. Further, some of such embodiments only correct slicelocations. Since the subject position and orientation is assumed to bestatic between a given “excitation” and “readout”, such a scheme canwork well for relatively slow movements, on the order of a fewmillimeters/second. However, more rapid movements require dynamicupdates of sequence parameters (for instance every few milliseconds)between excitation and acquisition, i.e. within each line of k-space. Ofnote, some tracking techniques, such as optical techniques, can allowvery rapid and accurate tracking, from 100 to up to 1000 times persecond.

Consequently, updating scan parameters “intra-scan” as described hereincan allow compensation of even the most rapid movements, up to 10 s or100 s of mm/second or even higher. Therefore, rapidly repeated motioncorrection with “intra-scan” updates as described herein makes itpossible to perform high-quality MR scans in very sick or confusedsubjects or children, without the need for anesthesia.

Importantly, the concepts described herein can generally be applied toany imaging or spectroscopy sequence and therefore can constitute auniversal method to compensate the effects of subject motion in any MRscan. For some spectroscopy scans, data may not be acquired in k-space(i.e. without use of readout gradients); however, the methods disclosedcan be used to eliminate phase errors and/or imbalances in gradientmoments due to motion, which otherwise result in signal reduction andspectral distortions due to non coherent averaging of signals. Likewise,some imaging techniques use non-rectangular sampling in k-space, but themethods described can easily be adapted to such sampling schemes.

Computing System

In some embodiments, the computer clients and/or servers described abovetake the form of a computing system 1100 illustrated in FIG. 11, whichis a block diagram of one embodiment of a computing system that is incommunication with one or more computing systems 1110 and/or one or moredata sources 1120 via one or more networks 1116. The computing system1100 may be used to implement one or more of the systems and methodsdescribed herein. In addition, in one embodiment, the computing system1100 may be configured to apply one or more of the intra-scan motioncorrection techniques described herein. While FIG. 11 illustrates oneembodiment of a computing system 1100, it is recognized that thefunctionality provided for in the components and modules of computingsystem 1100 may be combined into fewer components and modules or furtherseparated into additional components and modules.

Motion Correction Module

In one embodiment, the system 1100 comprises a motion correction module1106 that carries out the functions described herein with reference torepeatedly correcting motion effects during a scan, including any one ofthe intra-scan motion correction techniques described above. The motioncorrection module 1106 may be executed on the computing system 1100 by acentral processing unit 1102 discussed further below.

In general, the word “module,” as used herein, refers to logic embodiedin hardware or firmware, or to a collection of software instructions,possibly having entry and exit points, written in a programminglanguage, such as, for example, COBOL, CICS, Java, Lua, C or C++. Asoftware module may be compiled and linked into an executable program,installed in a dynamic link library, or may be written in an interpretedprogramming language such as, for example, BASIC, Perl, or Python. Itwill be appreciated that software modules may be callable from othermodules or from themselves, and/or may be invoked in response todetected events or interrupts. Software instructions may be embedded infirmware, such as an EPROM. It will be further appreciated that hardwaremodules may be comprised of connected logic units, such as gates andflip-flops, and/or may be comprised of programmable units, such asprogrammable gate arrays or processors. The modules described herein arepreferably implemented as software modules, but may be represented inhardware or firmware. Generally, the modules described herein refer tological modules that may be combined with other modules or divided intosub-modules despite their physical organization or storage.

Computing System Components

In one embodiment, the computing system 1100 also comprises a mainframecomputer suitable for controlling and/or communicating with largedatabases, performing high volume transaction processing, and generatingreports from large databases. The computing system 1100 also comprises acentral processing unit (“CPU”) 1102, which may comprise a conventionalmicroprocessor. The computing system 1100 further comprises a memory1104, such as random access memory (“RAM”) for temporary storage ofinformation and/or a read only memory (“ROM”) for permanent storage ofinformation, and a mass storage device 1108, such as a hard drive,diskette, or optical media storage device. Typically, the modules of thecomputing system 1100 are connected to the computer using a standardsbased bus system. In different embodiments, the standards based bussystem could be Peripheral Component Interconnect (PCI), Microchannel,SCSI, Industrial Standard Architecture (ISA) and Extended ISA (EISA)architectures, for example.

The computing system 1100 comprises one or more commonly availableinput/output (I/O) devices and interfaces 1112, such as a keyboard,mouse, touchpad, and printer. In one embodiment, the I/O devices andinterfaces 1112 comprise one or more display devices, such as a monitor,that allows the visual presentation of data to a user. Moreparticularly, a display device provides for the presentation of GUIs,application software data, and multimedia presentations, for example. Inthe embodiment of FIG. 11, the I/O devices and interfaces 1112 alsoprovide a communications interface to various external devices. Thecomputing system 1100 may also comprise one or more multimedia devices1110, such as speakers, video cards, graphics accelerators, andmicrophones, for example.

Computing System Device/Operating System

The computing system 1100 may run on a variety of computing devices,such as, for example, a server, a Windows server, an Structure QueryLanguage server, a Unix server, a personal computer, a mainframecomputer, a laptop computer, a cell phone, a personal digital assistant,a kiosk, an audio player, and so forth. The computing system 1100 isgenerally controlled and coordinated by operating system software, suchas z/OS, Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP,Windows Vista, Windows 7, Linux, BSD, SunOS, Solaris, or othercompatible operating systems. In Macintosh systems, the operating systemmay be any available operating system, such as MAC OS X. In otherembodiments, the computing system 5800 may be controlled by aproprietary operating system. Conventional operating systems control andschedule computer processes for execution, perform memory management,provide file system, networking, and I/O services, and provide a userinterface, such as a graphical user interface (“GUI”), among otherthings.

Network

In the embodiment of FIG. 11, the computing system 1100 is coupled to anetwork 1116, such as a LAN, WAN, or the Internet, for example, via awired, wireless, or combination of wired and wireless, communicationlink 1114. The network 1116 communicates with various computing devicesand/or other electronic devices via wired or wireless communicationlinks. In the embodiment of FIG. 11, the network 1116 is communicatingwith one or more computing systems 1118 and/or one or more data sources1120.

Access to the image construction module 1106 of the computer system 1100by computing systems 1118 and/or by data sources 1120 may be through aweb-enabled user access point such as the computing systems' 1118 ordata source's 1120 personal computer, cellular phone, laptop, or otherdevice capable of connecting to the network 1116. Such a device may havea browser module is implemented as a module that uses text, graphics,audio, video, and other media to present data and to allow interactionwith data via the network 1116.

The browser module may be implemented as a combination of an all pointsaddressable display such as a cathode-ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, or other types and/or combinations ofdisplays. In addition, the browser module may be implemented tocommunicate with input devices 1112 and may also comprise software withthe appropriate interfaces which allow a user to access data through theuse of stylized screen elements such as, for example, menus, windows,dialog boxes, toolbars, and controls (for example, radio buttons, checkboxes, sliding scales, and so forth). Furthermore, the browser modulemay communicate with a set of input and output devices to receivesignals from the user.

The input device(s) may comprise a keyboard, roller ball, pen andstylus, mouse, trackball, voice recognition system, or pre-designatedswitches or buttons. The output device(s) may comprise a speaker, adisplay screen, a printer, or a voice synthesizer. In addition a touchscreen may act as a hybrid input/output device. In another embodiment, auser may interact with the system more directly such as through a systemterminal connected to the score generator without communications overthe Internet, a WAN, or LAN, or similar network.

In some embodiments, the system 1100 may comprise a physical or logicalconnection established between a remote microprocessor and a mainframehost computer for the express purpose of uploading, downloading, orviewing interactive data and databases on-line in real time. The remotemicroprocessor may be operated by an entity operating the computersystem 1100, including the client server systems or the main serversystem, an/or may be operated by one or more of the data sources 1120and/or one or more of the computing systems. In some embodiments,terminal emulation software may be used on the microprocessor forparticipating in the micro-mainframe link.

In some embodiments, computing systems 1118 who are internal to anentity operating the computer system 1100 may access the imageconstruction module 1106 internally as an application or process run bythe CPU 1102.

User Access Point

In an embodiment, a user access point or user interface 1112 comprises apersonal computer, a laptop computer, a cellular phone, a GPS system, aBlackberry® device, a portable computing device, a server, a computerworkstation, a local area network of individual computers, aninteractive kiosk, a personal digital assistant, an interactive wirelesscommunications device, a handheld computer, an embedded computingdevice, or the like.

Other Systems

In addition to the systems that are illustrated in FIG. 11, the network1116 may communicate with other data sources or other computing devices.The computing system 1100 may also comprise one or more internal and/orexternal data sources. In some embodiments, one or more of the datarepositories and the data sources may be implemented using a relationaldatabase, such as DB2, Sybase, Oracle, CodeBase and Microsoft® SQLServer as well as other types of databases such as, for example, asignal database, object-oriented database, and/or a record-baseddatabase.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment. Theheadings used herein are for the convenience of the reader only and arenot meant to limit the scope of the inventions or claims.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. Additionally, the skilled artisan will recognize that any ofthe above-described methods can be carried out using any appropriateapparatus. Further, the disclosure herein of any particular feature,aspect, method, property, characteristic, quality, attribute, element,or the like in connection with an embodiment can be used in all otherembodiments set forth herein. For all of the embodiments describedherein the steps of the methods need not be performed sequentially.Thus, it is intended that the scope of the present invention hereindisclosed should not be limited by the particular disclosed embodimentsdescribed above.

1-186. (canceled)
 187. A magnetic resonance system configured to correctintra-scan motion during a magnetic resonance scan, the systemcomprising: a magnetic resonance scanner configured to: apply at least afirst pulse sequence comprising one or more RF pulses; and generate amagnetic field gradient comprising a correction gradient; a motiontracking system configured to: detect motion of a subject; and generatemotion data corresponding to the motion of the subject; one or morecomputer readable storage devices configured to store one or moremodules, the one or more modules including a correction gradientcalculation module; and one or more hardware computer processors incommunication with the one or more computer readable storage devices andconfigured to execute the one or more modules to cause the magneticresonance scanner to: generate the correction gradient, the correctiongradient being generated based on at least a first gradient moment,wherein the first gradient moment is calculated by the correctiongradient calculation module based on at least an integral of the motiondata and the one or more RF pulses of the first pulse sequence, andapply the correction gradient to the subject after all of the one ormore RF pulses are applied to the subject but prior to detecting signalsemitted from the subject in response to the application of all of theone or more RF pulses and the correction gradient, to prospectivelycorrect one or more errors in the first gradient moment due to movementof the subject during the magnetic resonance scan; and detect thesignals emitted from the subject in response to the application of allof the one or more RF pulses and the correction gradient for dataacquisition.
 188. The magnetic resonance system of claim 187, whereinthe correction gradient is an additional magnetic gradient to be appliedto the subject for a period of time.
 189. The magnetic resonance systemof claim 187, wherein the correction gradient is applied in conjunctionwith another gradient.
 190. The magnetic resonance system of claim 187,wherein the one or more modules further includes a phase encoding moduleconfigured to update one or more phase encoding gradients based on themotion data, wherein the phase encoding gradient is configured to beapplied immediately prior to data acquisition.
 191. The magneticresonance system of claim 187, wherein the one or more modules furtherincludes a read encoding gradient update module configured to update oneor more read encoding gradients based on the motion data.
 192. Themagnetic resonance system of claim 191, wherein the read encoding updatemodule is configured to update the one or more read encoding gradientsafter application of all of the one or more RF pulses but prior todetecting signals emitted from the subject in response to theapplication of all of the one or more RF pulses and the correctiongradient.
 193. The magnetic resonance system of claim 191, wherein theread encoding update module is configured to update the one or more readencoding gradients concurrently with detecting signals emitted from thesubject in response to the application of all of the one or more RFpulses and the correction gradient.
 194. The magnetic resonance systemof claim 187, further comprising a geometry update module configured toupdate geometric data based on the motion data to correct errors in thegeometric data due to movement of the subject, wherein the geometricupdate module is configured to update the geometric data prior to an RFpulse of the one or more RF pulses, and wherein the correction gradientis configured to be applied to the subject after all of the one or moreRF pulses are applied to the subject and all of the geometric dataupdates are applied.
 195. The magnetic resonance system of claim 194,wherein the geometry update module is configured to update the geometricdata prior to each RF pulse.
 196. The magnetic resonance system of claim187, wherein the correction gradient is further configured to be appliedto the subject immediately prior to detecting signals emitted from thesubject for data acquisition.
 197. A computer-readable, non-transitorystorage medium having a computer program stored thereon for causing asuitably programmed computer system to process by one or more processorscomputer-program code by performing a method for correcting intra-scanmotion during a magnetic resonance scan when the computer program isexecuted on the suitably programmed computer system, the methodcomprising: causing a magnetic resonance scanner to apply at least afirst pulse sequence comprising one or more RF pulses, wherein themagnetic resonance scanner is configured to generate a magnetic fieldgradient comprising a correction gradient; receiving electronic motiondata from a motion tracking system, wherein the motion tracking systemis configured to detect motion of a subject and generate the motion datacorresponding to the motion of the subject; generating, by a correctiongradient calculation module, the correction gradient, the correctiongradient being generated based on at least a first gradient moment,wherein the first gradient moment is calculated by the correctiongradient calculation module based on at least an integral of the motiondata and the one or more RF pulses of the first pulse sequence; andcausing, by the computer system, the magnetic resonance scanner to applythe correction gradient to the subject after all of the one or more RFpulses are applied to the subject but prior to detecting signals emittedfrom the subject in response to the application of all of the one ormore RF pulses and the correction gradient, to prospectively correct oneor more errors in the first gradient moment due to movement of thesubject during the magnetic resonance scan; and causing, by the computerprogram, the magnetic resonance scanner to detect the signals emittedfrom the subject in response to the application of all of the one ormore RF pulses and the correction gradient for data acquisition, whereinthe computer system comprises a computer processor and electronicmemory.
 198. The computer-readable, non-transitory storage medium ofclaim 197, wherein the correction gradient is an additional magneticgradient to be applied to the subject for a period of time.
 199. Thecomputer-readable, non-transitory storage medium of claim 197, whereinthe correction gradient is applied in conjunction with another gradient.200. The computer-readable, non-transitory storage medium of claim 197,wherein the method further comprises updating, by a phase encodingmodule, one or more phase encoding gradients based on the motion data,and wherein the phase encoding gradient is configured to be appliedimmediately prior to data acquisition.
 201. The computer-readable,non-transitory storage medium of claim 197, wherein the method furthercomprises updating, by a read encoding gradient update module, one ormore read encoding gradients based on the motion data.
 202. Thecomputer-readable, non-transitory storage medium of claim 201, whereinthe read encoding update module is configured to update the one or moreread encoding gradients after application of all of the one or more RFpulses but prior to detecting signals emitted from the subject inresponse to the application of all of the one or more RF pulses and thecorrection gradient.
 203. The computer-readable, non-transitory storagemedium of claim 201, wherein the read encoding update module isconfigured to update the one or more read encoding gradientsconcurrently with detecting signals emitted from the subject in responseto the application of all of the one or more RF pulses and thecorrection gradient.
 204. The computer-readable, non-transitory storagemedium of claim 197, wherein the method further comprises updating, by ageometry update module, geometric data based on the motion data tocorrect errors in the geometric data due to movement of the subject,wherein the geometric update module is configured to update thegeometric data prior to an RF pulse of the one or more RF pulses, andwherein the correction gradient is configured to be applied to thesubject after all of the one or more RF pulses are applied to thesubject and all of the geometric data updates are applied.
 205. Thecomputer-readable, non-transitory storage medium of claim 204, whereinthe geometry update module is configured to update the geometric dataprior to each RF pulse.
 206. The computer-readable, non-transitorystorage medium of claim 197, wherein the correction gradient is furtherconfigured to be applied to the subject immediately prior to detectingsignals emitted from the subject for data acquisition.